JSFiddle - React, Tailwind, and code Playground

JavaScript

function rxGroups(rx, str) {
       var matches = new Array();
       match = rx.exec(str);
       while (match != null) {
          matches.push(match[1]);
          match = rx.exec(str);
       }
       return matches;
    }
    
    var x = rxGroups(
       /\((.+?)\)/ig,
       "Key (email)=([email protected]) already exists"
    );

    alert(x.join('\n'));